1. Technical Field
The present invention relates to a liquid crystal device and an electronic apparatus.
2. Related Art
A liquid crystal device has been known as a display device. The liquid crystal device is, for example, provided with a liquid crystal panel and a backlight that supplies light to the liquid crystal panel.
The liquid crystal panel includes an element substrate, an opposite substrate that is opposed to the element substrate, and a liquid crystal provided between the element substrate and the opposite substrate.
The element substrate includes a plurality of scanning lines and a plurality of auxiliary capacitor lines that are alternately provided at predetermined intervals, a plurality of data lines that intersect with the plurality of scanning lines and the plurality of auxiliary capacitor lines and that are provided at predetermined intervals, a scanning line driving circuit connected to the plurality of scanning lines, a data line driving circuit connected to the plurality of data lines, and a control circuit that is connected to the plurality of auxiliary capacitor lines and that drives the auxiliary capacitor lines.
Pixels are provided at positions corresponding to intersections of the scanning line and the data lines. Each of the pixels includes a pixel capacitor, a thin film transistor (hereinafter, referred to as TFT), and a storage capacitor (auxiliary capacitor). The pixel capacitor is formed of a pixel electrode and a common electrode. The thin film transistor serves as a switching element. One electrode (auxiliary capacitor electrode) of the storage capacitor is connected to the capacitor line and the other electrode is connected to the pixel electrode. The plurality of pixels are arranged in a matrix to form a display area.
The gate of the TFT is connected to the scanning line, the source of the TFT is connected to the data line and the drain of the TFT is connected to the pixel electrode and the other electrode of the auxiliary capacitor.
A capacitor line driving circuit supplies a predetermined voltage to each capacitor line.
The scanning line driving circuit supplies each scanning line with a selection voltage that selects the scanning line in a predetermined order. As a selection voltage is supplied to a scanning line, the TFTs connected to the scanning line all enter an on state.
The data line driving circuit supplies an image signal to each data line and writes an image voltage based on the image signal to the pixel electrode through the TFT, which is in an on state.
Here, the data line driving circuit alternately performs positive polarity writing and negative polarity writing. In the positive polarity writing, the data line driving circuit supplies the data lines with image signals of voltages that are higher in electric potential than the voltage of the common electrode (hereinafter, referred to as positive polarity) to thereby write the pixel electrodes with image voltages based on the positive polarity image signals. In the negative polarity writing, the data line driving circuit supplies the data lines with image signals of voltages that are lower in electric potential than the voltage of the common electrode (hereinafter, referred to as negative polarity) to thereby write the pixel electrodes with image voltages based on the negative polarity image signals.
The opposite substrate includes color filters, such as R (red), G (green) and B (blue), corresponding to the pixels.
The above described liquid crystal device operates as follows.
That is, by sequentially supplying a selection voltage to the scanning lines, all the TFTs connected to one scanning line are made to enter an on state to thereby select all the pixels associated with this scanning line. Then, in synchronization with selection of these pixels, image signals are supplied to the data lines. Then, image signals are supplied to all the selected pixels through the TFTs, which are in an on state, and image voltages based on the image signals are written to the pixel electrodes.
As the image voltage is written to the pixel electrode, a liquid crystal is applied with a driving voltage because of a difference in electric potential between the pixel electrode and the common electrode. As the driving voltage is applied to the liquid crystal, alignment and/or order of the liquid crystal change and, as a result, light emitted from a backlight and transmitted through the liquid crystal varies. Grayshade is performed in such a manner that the above varied light is transmitted through a color filter.
Note that the driving voltage applied to the liquid crystal is held, owing to an auxiliary capacitor, during a period of time that is three digits longer than a period of time during which an image voltage is being written.
Incidentally, the above described liquid crystal device is, for example, used for a cellular phone and, in recent years, there is a need for the cellular phone to reduce power consumption. Then, there has been proposed a liquid crystal device that is able to reduce power consumption by performing capacitor line swing driving, which is a so-called SSL (Swing Storage Line), in which, after an image voltage has been written to the pixel electrode, the TFT is made to enter an off state and, in addition, an auxiliary capacitor voltage (VST) of an auxiliary capacitor line is changed from a high electric potential (VSTH) to a low electric potential (VSTL) or changed from a low electric potential to a high electric potential, which is, for example, described in JP-A-2002-196358.
In addition, a lateral electric field mode liquid crystal device includes an IPS (In-Plane Switching) liquid crystal device or an FFS (Fringe-Field Switching) liquid crystal device, which is provided with pixel electrodes and a common electrode, which form pixel capacitors, formed on one of a pair of substrates that hold the liquid crystal. In the lateral electric field mode liquid crystal device, a common electrode (COM electrode) also serves as an auxiliary capacitor electrode and, then, a pixel capacitor and an auxiliary capacitor are integrally formed. A liquid crystal device, which has been proposed by the applicant of the present application, is able to reduce power consumption and also able to suppress deterioration of display quality in such a manner that the capacitor line swing driving in the lateral electric field mode, in which, after the common electrode has been supplied with a voltage having a high electric potential (VCOMH) or a voltage having a low electric potential (VCOML), a negative polarity image signal or a positive polarity image signal is supplied to the data line, is performed.
The circuit of the above described capacitor line swing driving or COM separate driving is formed on a glass substrate using a technology termed SOG (system on glass). In the above described circuit, in order to have an image display based on a positive polarity image signal or a negative polarity image signal reliably work using a transistor formed on the substrate, a power source that drives the transistor uses 8 V as a positive power source and −4 V as a negative power source, and a voltage Vgs between the gate and source of the transistor is 12 V at the maximum. Thus, the gate length (hereinafter, referred to as L length) of the transistor has been set to an L length of a size by which the Vgs 12 V may be used without any problem.
Here, because a capacitor line or a common line is influenced by a parasitic capacitance that is generated at a portion at which the capacitor line or the common line intersects with a data line, as a measure to crosstalk, it is desirable that a transistor that supplies the capacitor line or the common line with a high electric potential or a low electric potential has a low on resistance. However, when the maximum value of the Vgs is large, the L length of the transistor also needs to be increased. Thus, there has been a problem that the on resistance of the transistor increases as the L length increases. Furthermore, when the on resistance of the transistor is large and, therefore, a crosstalk becomes problematic, it is necessary to reduce the resistance of the circuit by increasing the width of the line connected to the transistor to reduce its resistance so as to prevent the occurrence of a crosstalk. Thus, the area of the circuit becomes large and, as a result, it has been an obstacle to a reduction in window frame region in which driving circuits are formed (around a pixel region) and/or a reduction in power consumption.